When I was a kid, I would always keep goldfish in the tiny bowls and cleaned it whenever I wanted to. Than I would wonder why they died.lol I took down my 5G when I lost my "King" betta and I would rather not put that up again (my sister hated it). I would like to get the smallest goldfish...can one be kept in a 2.5G? I know I would have to clean it a lot because they poop a lot. I also wouldn't use a filter (I don't use filters for my bettas) so would that be ok or do they need a filter or bubbler? Sorry, I know NOTHING about goldfish other than they like cold water.lol 8) Any input would be great, thanks!

There is no adult Goldfish that can live in an unfiltered 5gl or a 2.5gl. Unless someone has invented a pygmy dwarf version and forgot to tell me about it, lol.

Have a look at this: http://en.wikipedia.org/wiki/Goldfish
After reading this article, it seems that even the smaller species still attain lengths of 5" to 8", which is much, much too large for the tank you are considering.

I hate to be the bearer of bad news, but that will most definitely not work out. A goldfish cannot live in a tank so small, especially without a filter. Although a goldfish may look small when it's young, they can grow extremely fast. You would need to invest in a much bigger aquarium if you wanted to get a goldfish.

I can go into more detail if you'd like, but I believe I speak for most people on this forum when I advise you that this will not work out. For a tank that small, I would recommend sticking with a betta, and even considering investing in a filter.

i tried that only with two black moor goldfish. Needless to say i eventually got lazy and forgot to clean the tank out as often as i needed to. Then they both got sick so i cleaned the tank and gave them medicine annnnd everything was honky dory until i came home from school one day they were both dead :( I loved them though, their names were kanyé and beyoncé haha